Cooling tower systems are subjected to stress during their operation. Two stresses are mineral scale buildup and pH variances in the cooling water system. Specifically, as the water in a cooling system dissipates heat by evaporation, the components of mineral scale in the remaining water become more concentrated, causing precipitation of the mineral scale on the internals of the cooling tower system, creating operational problems. Adding to the problem is the desorption of carbon dioxide, which results in an increase in pH.
A conductivity meter is usually used to monitor the potential for mineral scale buildup in a cooling tower system. When the cooling tower system cycles up, the concentration of ions such as Ca++ and Mg++ increase in concentration. To combat this stress the cooling tower system is blown down and makeup water is added back into the system.
The pH of water in cooling tower systems is often controlled by the injection of a strong acid, resulting in reduction of the saturation level of pH sensitive mineral scales. Although the addition of a strong acid is inexpensive and simple, this methodology has many disadvantages which include the following: (1) a malfunction of the controller can result in acid overfeed, producing an acidic water, which can cause severe corrosion damage to the system; (2) the addition of a strong acid results in a buildup of the counter ion of the acid, which can contribute to other forms of scaling and to corrosion; (3) operation of the pH control system requires the handling of strong acids such as dangerous mineral acids; and (4) cations such as Ca++ and Mg++ which also contribute to scale formation are not removed from the system.
An efficient protocol for controlling a cooling system that deals with both pH and mineral/scale buildup is thus desired.